# hmac_sign_verify

utilpeek: Returns the HMAC of a message under a shared key (sign), or whether a signature matches it in constant time (verify); handles GitHub (sha256= prefix accepted), Stripe v1 (of {t}.{raw body}) and Slack v0 (of v0:{timestamp}:{raw body}) webhook signatures. For plain digests use hash_text; for JWTs use verify_jwt. Input: mode, message, key, optional key_encoding, algorithm, output and, for verify, signature. Malformed hex or base64, a sha*= prefix naming another algorithm, or verify without a signature is a 422 (not charged). Other prefixes (v0=, v1=) are not stripped. sha1 is for legacy webhooks only. The key and message are never echoed. Typically under 0.1 s. Price: USD 0.001. Free: 10 utilpeek calls per IP per UTC day. The submitted text is never logged or stored. Docs: https://tanod.dev/learn/verify-webhook-signature-hmac-api.html

Agent View of the PolicyLayer registry record for `hmac_sign_verify`. HTML page: https://policylayer.com/tools/dev-tanod-tanod/hmac-sign-verify

## Facts

- Tool: `hmac_sign_verify`
- Server: Tanod (`https://tanod.dev/mcp`) — https://policylayer.com/tools/dev-tanod-tanod.md
- Homepage: https://github.com/https://tanod.dev/mcp
- Risk category: Read (Low risk)
- Registry record: grade F, identity unverified
- Server auth posture: open
- Server CORS policy: *
- Server rate-limited: no
- Parameters: 7 (3 required)
- Recommended policy verdict: Allowed

## Parameters

| Parameter | Type | Required | Description |
| --- | --- | --- | --- |
| `key` | string | yes | The shared secret (at most 1 KiB), read as `key_encoding`. Never echoed or logged. |
| `mode` | string | yes | sign (compute the HMAC) or verify (check `signature`). |
| `output` | string | no | Signature encoding: hex (default) or base64. |
| `message` | string | yes | The signed payload exactly as received (e.g. the raw webhook body), as text; at most 64 KiB as UTF-8. |
| `algorithm` | string | no | sha256 (default), sha512, or sha1 (legacy webhooks only). |
| `signature` | object | no | verify only: the signature to check, in `output` encoding. A `sha256=` style prefix (GitHub's X-Hub-Signature-256) is stripped when it names `algorithm`. |
| `key_encoding` | string | no | utf8 (default), hex or base64 (standard alphabet). |

Parameters from the server's own tool schema.

## Example call (MCP tools/call, JSON-RPC 2.0)

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "hmac_sign_verify",
    "arguments": {
      "key": "<key>",
      "mode": "<mode>",
      "message": "<message>"
    }
  }
}
```

## Why hmac_sign_verify is rated Low

Even though hmac_sign_verify only reads data, uncontrolled read access leaks sensitive information and racks up API costs: an agent caught in a retry loop can make thousands of calls a minute without anyone noticing.

## Use case

AI agents call hmac_sign_verify to retrieve information from Tanod without modifying anything. It is typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.

## Recommended policy (PolicyLayer)

Verdict: **Allowed**. Enforced by the PolicyLayer MCP gateway (https://policylayer.com/mcp-gateway) before a call reaches Tanod:

```json
{
  "version": "1",
  "default": "deny",
  "tools": {
    "hmac_sign_verify": {}
  }
}
```

## Other tools on Tanod (307)

- `audit_token_approvals` — Destructive — https://policylayer.com/tools/dev-tanod-tanod/audit-token-approvals.md
- `aurora_forecast` — Destructive — https://policylayer.com/tools/dev-tanod-tanod/aurora-forecast.md
- `diff_text` — Destructive — https://policylayer.com/tools/dev-tanod-tanod/diff-text.md
- `image_metadata` — Destructive — https://policylayer.com/tools/dev-tanod-tanod/image-metadata.md
- `pdf_pipeline` — Destructive — https://policylayer.com/tools/dev-tanod-tanod/pdf-pipeline.md
- `pdf_protect` — Destructive — https://policylayer.com/tools/dev-tanod-tanod/pdf-protect.md
- `pdf_remove_pages` — Destructive — https://policylayer.com/tools/dev-tanod-tanod/pdf-remove-pages.md
- `pdf_reorder_pages` — Destructive — https://policylayer.com/tools/dev-tanod-tanod/pdf-reorder-pages.md
- `build_ics_event` — Execute — https://policylayer.com/tools/dev-tanod-tanod/build-ics-event.md
- `build_pptx_deck` — Execute — https://policylayer.com/tools/dev-tanod-tanod/build-pptx-deck.md
- `build_xlsx_workbook` — Execute — https://policylayer.com/tools/dev-tanod-tanod/build-xlsx-workbook.md
- `bulk_agent_index` — Execute — https://policylayer.com/tools/dev-tanod-tanod/bulk-agent-index.md
- `cron_next_runs` — Execute — https://policylayer.com/tools/dev-tanod-tanod/cron-next-runs.md
- `decode_calldata` — Execute — https://policylayer.com/tools/dev-tanod-tanod/decode-calldata.md
- `expand_rrule` — Execute — https://policylayer.com/tools/dev-tanod-tanod/expand-rrule.md
- `html_to_pdf` — Execute — https://policylayer.com/tools/dev-tanod-tanod/html-to-pdf.md
- `image_crop` — Execute — https://policylayer.com/tools/dev-tanod-tanod/image-crop.md
- `parse_ics` — Execute — https://policylayer.com/tools/dev-tanod-tanod/parse-ics.md
- `parse_phone_number` — Execute — https://policylayer.com/tools/dev-tanod-tanod/parse-phone-number.md
- `parse_rss_feed` — Execute — https://policylayer.com/tools/dev-tanod-tanod/parse-rss-feed.md
- `parse_sitemap` — Execute — https://policylayer.com/tools/dev-tanod-tanod/parse-sitemap.md
- `parse_url` — Execute — https://policylayer.com/tools/dev-tanod-tanod/parse-url.md
- `parse_user_agent` — Execute — https://policylayer.com/tools/dev-tanod-tanod/parse-user-agent.md
- `render_mermaid` — Execute — https://policylayer.com/tools/dev-tanod-tanod/render-mermaid.md
- `satellite_passes` — Execute — https://policylayer.com/tools/dev-tanod-tanod/satellite-passes.md
- `sec_financials` — Execute — https://policylayer.com/tools/dev-tanod-tanod/sec-financials.md
- `transcribe_audio` — Execute — https://policylayer.com/tools/dev-tanod-tanod/transcribe-audio.md
- `x402_well_known_file` — Execute — https://policylayer.com/tools/dev-tanod-tanod/x402-well-known-file.md
- `compare_stablecoin_transfer_fees` — Financial — https://policylayer.com/tools/dev-tanod-tanod/compare-stablecoin-transfer-fees.md
- `transfer_preflight` — Financial — https://policylayer.com/tools/dev-tanod-tanod/transfer-preflight.md
- …and 277 more: https://policylayer.com/tools/dev-tanod-tanod.md

## For agents

This record is a snapshot. Live verdicts and the full registry:

- Check every server in your MCP config at once: `npx -y policylayer stack`
- Vet a server before you add it: install the mcp-precheck skill — `npx skills add https://policylayer.com` (skill text: https://policylayer.com/skill.md)
- Query the registry over MCP: endpoint `https://api.policylayer.com/mcp` — tools `check_mcp_server`, `check_mcp_stack`, `check_tool`, `search_registry`, `get_change_events`

---

Source: the PolicyLayer MCP registry — one continuously verified record per MCP server. Full record: https://policylayer.com/registry?q=dev-tanod-tanod · API: https://policylayer.com/registry/api · Policy library: https://policylayer.com/policies/dev-tanod-tanod